The present invention relates to a pressure control valve of the type having a pilot poppet therein.
Relief valves capable of controlling a pressure in a hydraulic fluid circuit to below a predetermined reference value may generally be classified into two types, i.e., one which directly responds to a relationship between the circuit pressure and a preload of a spring, and a second type which has a pilot valve and responds to an amplified pressure differential. The present invention is concerned with the second type of relief valve which permits subtle adjusment of a reference pressure and, therefore, a highly accurate control of the fluid pressure.
Generally, a relief valve of the type described has a relief function and a void control or so-called "anti-void" function. The relief function is such that, when the pressure in a hydraulic fluid circuit exceeds a predetermined reference level, a pressure passageway leading from a cylinder port or the like is communicated to a relief passageway to relieve part of the fluid, thereby controlling the pressure in the pressure passageway to the reference level. The anti-void function, on the other hand, is such that upon lowering of the circuit pressure beyond the reference level due to cavitation in the pressure passageway or the like, the pressure passageway and relief passageway are communicated to each other to suck a sufficient amount of fluid from the relief passageway to the pressure passageway to fill up the resulting void, thus maintaining the pressure in the pressure passageway at the reference level. The relief valve has a back pressure chamber defined by a check poppet received in a housing, a valve body screwed into the housing with its end slidably received in the check poppet, and a relief valve slidable within the check poppet.
Commonly utilizing a fluid pressure in the back pressure chamber, the relief function occurs by suitably controlling the relief poppet while the anti-void function occurs by suitably controlling the check poppet. However, the common use of the pressure in the back pressure chamber causes the two different performances to conflict with each other; improving one of the performances deteriorates the other. Particularly, the response of the valve for the anti-void function is slowed down to rather promote the cavitation.
Another problem heretofore pointed out is that a main flow of fluid led from the pressure passageway to the relief passageway through holes in the check poppet affects a pilot flow directed to the relief passageway through a pilot passageway, in a position of the valve where the former joins the latter. The result is unstable relief actions which constitutes a source of high frequency vibration or noise.